Oscillation generator



5, 1936. A. M. BRAATEN 2,051,936

OSCILLATION GENERATOR.

Filed May :5, 1935 INVENTOR ARTHUR M. BRAATEN ATTORNEY wherein,

.potential to the tube oscillator; and,

UNITED STATES PATENT OFFICE OSCILLATION GENERATOR Arthur M. Braaten,Riverhead, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application May 3, 1933, Serial No. 669,269

5 Claims.

This invention relates to the vacuum tube oscillator art and deals morespecifically with a piezo-electric controlled, negative resistanceoscillator.

Heretofore it has been the practice to use a three or four-elementvacuum tube operating on the dynatron principle to supply oscillationsof fairly constant stability. The output of such an oscillator, having ahigh harmonic content, has been used to provide a series of harmonicfrequencies in frequency meters, or wherever such an output was desired.However, one disadvantage which limits the usefulness of suchoscillators is that the frequency of oscillation depends to a greatextent upon the supply voltages and the output loading. To improve thefrequency stability of such systems and to provide a better means ofobtaining harmonic outputs of the desired order arevprincipal objects ofmy present invention. A further object of my invention is to provide agreater degree of. frequency stability .for an oscillator operating onthe dynatron principle, and to provide an efficient and moresatisfactory method for making use of the output of such an oscillator.g

A further objectofmy present invention is to provide a dynatronoscillator circuit together with an arrangement or circuit in whichpower output may be derived therefrom without effecting the frequency ofoperation of the dynatron oscillator.

My invention is described in greater detail in connection with theaccompanying drawing Figure 1 illustrates a preferred form of myinvention wherein a piezo-electric crystal is utilizedto control thefrequency of a dynatron oscillator and whereinthe oscillator is renderedsubstantially immune to load reaction.

Figure 2 is a modification of the arrangement .shown in Figure 1;

Figures 3 and 4. are further modifications of f the arrangement shown inFigure 1 wherein different circuits are provided for supplying plateFigures 5 and 6 are still further alternative arrangements for reducingstill further the effects of load reaction upon my improved oscillationgenerator.

Referring to Figure 1, V.T. is a six-element vacuum tube of the heatertype. The cathode 2 and one side of the heater 4 are connected toground. The inner, or control, grid 6 is connected to ground through afixed resistor R. Across R is connected the piezo-electric element Q. C.The middle, or screen grid 8 is connected to a source of positivepotential, with respect to the cathode 2. The anode, or plate It! isconnected to a potential positive with respect to the screen grid 8. Inthe plate circuit is connected 5 a tuning circuit L2C2., Connectedbetween the outer, or suppressor, grid I2 and at a potential positivewith respect to the cathode and negative with respect to the screen gridis a tuning circuit L1C1. Variable condenser C is connected be- 10tweenvthe suppressor and control grids. The heater is energized by theusual battery l4. 7

The operation of, the system of Figure 1 is as follows:

Suppose the elements Q. 0., 0, L101 and L2C2 to be omitted from thecircuit. With certain positive fixed potentials on the screen grid andthe plate, if the potential on the suppressor grid is varied, a regionwill be found wherein the device acts as a true negative resistance.That is, an '20 appliedpotential will set up a current in the Wrongdirection. This is due to secondary emission from the suppressor grid. Adevice with such a negative resistance characteristic may be made toproduce sustained oscillations. If the tuned element L1C1 be adjusted sothat its effective resistance is equal tothe negative resistance of thesuppressor grid circuit, the total resistance of that circuit will bezero, and the device will produce sustained oscillations. In certaintypes 30 of tubes the negative resistance may be of such a high valuethat it is impossible tomake the .device. oscillate. In such a case, theaddition of a capacity C of suitable value between the control grid andthe suppressor grid will have the 35 effect of lowering the negativeresistance, so that the device will oscillate. If a crystal oscillatoris connected between control grid and cathode of this device and theelement L1C1 tuned to the natural resonant frequency of the crystal, the40 frequency of oscillation of the system will be maintained at thefrequency at which the crystal is oscillating. Small changes in'thevalues of L1 or C1, or other circuit constants, *will have negligibleeffect on the frequency of the system, 45 and a degree of stabilityagainst voltage supply variations will be obtained which is unattainablewithout the crystal control element. If now the element LzC'z isconnected inthe plate circuitof the device, this output circuit may betuned to the fundamental oscillation frequency or any of its harmonics.Tuning of this circuit will have a minimum effecton the oscillatorfrequency. It will thus be seen that in this device there isincorporated an oscillator of substantially constant frequency and. ameans for readily obtaining any desired harmonic of the fundamental inthe output, without the use of additional frequency multiplying stages.

Moreover, in connection with the arrangement shown in Figure 1, if theoutput is taken from the plate circuit CzLz, load reaction will besubstantially minimized and reduced to a negligible value therebyrendering the frequency of operation substantially independent thereof.

The circuit C1L1 is preferably tuned to a fundamental of the crystal Q.C. and the circuit C2L2 may be tuned to the same frequency or to aharmonic thereof. On the other hand the circuit C1L1 may be tuned to aharmonic of the crystal and circuit CzLz to the same harmonic, to adifferent harmonic, to a sub-harmonic, or to the fundamental.

Figure 2 illustrates a system quite similar to the one shown inconnection with Figure l but in this case the condenser C of Figure 1 isomitted since it is assumed that the vacuum tube V. T. is ofsufficiently low negative resistance to allow of oscillation generation.Also, in connection with Figure 2 by-passing condensers B. C. areprovided to ground the lower ends of the tuned circuits CILI and C2112.

The arrangement shown in Figure 3 is similar to that shown in Figure 1with the exception that the circuit C2L2 is blocked off from the directcurrent plate source P. S. by means of a blocking condenser 20. Platepotential is fed to the vacuum tube V. T. through the choke coil 22. Inthis manner a direct current component is kept from the tuned circuitCzLz of the vacuum tube V. T.

Figure 4 is similar to the arrangement shown in Figure 2 with theexception that the plate potential is fed through a resistor 22 and asin connection with Figure 3 the plate circuit CzLz is rendered immunefrom D. C. current flow by means of a blocking condenser 20.

The output circuit may be further isolated from the oscillating circuitas shown in Figure 5. Here the tuned circuit C1L1 is connected betweenthe heated element 3 of the cathode and ground. Moreover, a suppressorgrid I2 is grounded by means of a by-passing condenser 30 which, at veryhigh frequencies may be chosen of a value to series resonate with thelead to the suppressor grid I0 so as to effectively maintain thesuppressor at ground potential. Because of the circuit C1L1', thecathode 3 no longer operates at ground potential, but fluctuates atradio frequency potential. However, the suppressor grid I 2 ismaintained at ground radio frequency potential by the action ofby-passing condenser 30. This arrangement is advantageous since it moreeffectively isolates the oscillating circuit formed of the grids l2, 8,6, cathode 3 and quartz crystal from the output circuit C2L2 andhence'rendering the oscillating circuit or frequency controlling circuitless liable to frequency'shift from changes in load reaction. The outputenergy, of course, is obtained by virtue of the electron stream withinthe tube impinging upon the anode l0 and in turn exciting the paralleltuned circuit C2L2 which may be tuned to the same frequency as thecrystal or to some harmonic thereof. -The circuit ClLl may also be tunedto the same frequency as that of the crystal or to some harmonicthereof.

In the arrangement shown in Figure 6 a tuned circuit L303 is connectedbetween the intermediate grid or screen grid 8 and the cathode 3, thecircuit being completed by means of a radio frequency by-passingcondenser 40. The intermediate grid 8 besides causing secondary emissionfrom the suppressor grid I2 and hence dynatron action, acts as a platefor an oscillating system operating through regenerative action. Thisregenerative oscillating system is composed of the intermediate grid 8,the control grid 6 and the cathode 3. Condenser C is added only whenthere is insufficient capacity coupling between the grid 8 and controlgrid 6 to produce necessary feed back for sustained oscillationgeneration. Circuit C3L3 may be tuned to the fundamental of the quartzcrystal or to some harmonic frequency thereof. Similarly circuit L1C1may be tuned to the fundamental or to the same or different harmonic andlikewise with the circuit L2C2. Output energy at the same or differentfrequencies may be taken as indicated from any one or more of the'circuitsCiL1,-C3L3, or-CzLz simultaneously, or if desired only one ofthe circuits may be used'to supply oscillatory energy.

Incidentally, it is to be pointed out that while oscillations aregenerated in L101 by virtue of dynatron action which involves secondaryemission from suppressor grid l2, oscillations are generated in circuitLaCs by virtue of regenerative action or capacity feed back in the caseshown. In the circuit CzLz oscillations are produced by virtue'of thecoupling of that circuit to the other oscillating circuits C1L1 and 03L:through the medium of the electron stream within the vacuum tube V. T.

Considerable power may be obtained from the system contained in Figure 6and is capable of functioning as a master oscillator of extremely highfrequency'stability, as a buffer amplifier, and as a plurality offrequency multiplier stages, all at the same time.

Various minor changes may be made in all of the circuits which may beused for controlling the frequency of a transmitter for wave measurementpurposes, or for example, for use in a superheterodyne type of radioreceiver. Also, it should be understood that such circuits as L303 maybe replaced by an inductance whose natural frequency is higher than thatof a crystal, if it is desired to operate that portion of the circuit atthe fundamental frequency of the crystal and the output energy may betaken from any one or more of the various circuits in any of the figuresand used for different purposes if found desirable. Moreover, it will bereadily apparentthat in place of the, six element heater type of tube,

' a non-heater type of tube may be employed in any one of the systems.Also, the present invention is not to be limited to any specificarrangement of supply voltages but optimum voltages will be chosen witha view to produce a negative resistance characteristic. The crystal maybe of quartz or of any material exhibiting piezo-electric effects, or,may be replaced by an electrically tuned circuit, or by any magneticmechanical resonator as will be apparent to those skilled in the art.Instead of a common ground connection, any common conductor such as alarge piece of shielding may be used.

Having thus described my invention, what I claim is:

1. An oscillation generator comprising a vacuum tube having a cathode, acontrol grid, 2. screen grid, a suppressor grid and an anode, a highfrequency frequency controlling circuitincluding a piezo-electriccrystal connected between the control grid and cathode, a high frequencycircuit connected between the suppressor grid and cathode, means forpolarizing said suppressor and screen grids with unidirectionalpotential such that said vacuum tube has a negative resistancecharacteristic and continuous oscillations are set up in said circuitbetween said suppressor grid and said cathode, and a high frequencycircuit connected between said anode and said cathode, said highfrequency circuit being adapted to derive its excitation from theelectron coupling action between said anode and said oscillatory systemformed of said suppressor, screen and control grids, and cathode.

2. A vacuum tube oscillation generator comprising an electron dischargedevice having an anode, a cathode, a control grid, a screen grid, and asuppressor grid, a hi h frequency circuit connected between said controlgrid and cathode, a high frequency circuit connected between the screengrid and cathode, said control grid and screen grid being subjected topotentials such that oscillations are set up by virtue of regenerativecoupling between said screen grid and control grid, 2, high frequencycircuit connected between said suppressor grid and said cathode, meansfor polarizing said suppressor grid with respect to said screen grid andcathode as to cause oscillations to be set up in said circuit betweensaid suppressor grid and cathode by virtue of dynatron action, and, ahigh frequency circuit connected between said anode and cathode, saidanode being polarized such that oscillations are set up in said lastmentioned.

circuit by virtue of the coupling of said anode to said otheroscillating circuits by means of the electron stream within the vacuumtube.

3. Apparatus as claimed in the preceding claim wherein one of said highfrequency circuits is in the form of a p-iezo-electric crystal.

4. An oscillation generator comprising a tube having an anode, acathode, a first grid, 2. second grid, and a third grid, a frequencycontrolling circuit connected between the first grid and cathode, a highfrequency circuit connected between the third grid and cathode, meansfor polarizing said third grid to a direct current potential withrespect to said grid, means for polarizing said second grid to apositive potential with respect to said third grid and with respect tosaid cathode, whereby oscillations are set up in the circuit betweensaid third grid and cathode by virtue of negative resistance action,means for polarizing said anode to a direct current potential withrespect to said cathode, a high frequency circuit connected between saidanode and cathode, and means for deriving oscillations from said lastmentioned high frequency circuit, said oscillations being controlled infrequency by virtue of said frequency controlling circuit connectedbetween said first grid and cathode;

5. Apparatus as claimed in claim 4 characterized by the fact that saidfrequency controlling circuit includes a piezo-electricorystal and beingfurther characterized by the fact that at least one of said highfrequency circuits is tuned.

ARTHUR M. BRAATEN.

